Episodic eruptions of the Late Mesozoic volcanic sequences in southeastern Zhejiang, SE China: petrogenesis and implications for the geodynamics of paleo-Pacific subduction
Episodic eruptions of the Late Mesozoic volcanic sequences in southeastern Zhejiang, SE China: petrogenesis and implications for the geodynamics of paleo-Pacific subduction
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DOI：
10.1016/j.lithos.2012.07.002
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发表时间：
2012-12
期刊：
影响因子：
3.5
通讯作者：
Lei Liu;Xi‐sheng Xu;H. Zou
中科院分区：
文献类型：
--
作者：
Lei Liu;Xi‐sheng Xu;H. Zou
通过对浙东南晚中生代火山岩系锆石U-Pb和Hf同位素组成的系统测量，对火山岩系的形成时代和成因进行了研究。早燕山期（侏罗纪）火山作用发生在177 Ma，形成了区内零星分布的火山岩。燕山晚期（白垩纪）大规模的火山活动，在140 ~ 88 Ma之间，形成了广泛分布的上、下火山岩系，具有多期次喷发特征。在120- 110 Ma，下火山岩系与上火山岩系之间以及下火山岩系内两个细分旋回之间分别存在两个火山间断。此外，下统两个火山旋回的震级也有显著差异。下统第一旋回（140- 128 Ma）规模最大，远大于第二旋回（122- 120 Ma）和整个上统（110- 88 Ma）。广泛分布的晚中生代火山岩主要来源于古元古代地壳基底物质的部分熔融，122 Ma以后有明显的新生物质的加入。燕山早期火山岩中锆石的地壳模式年龄（TDM 2）主要为2.00-2.16Ga，εHf（t）加权平均值为-13.4。εHf（t）和TDM 2值为ca.第一旋回火山岩中锆石的年龄分别为-10和1.67-2.00Ga;第二旋回火山岩中锆石的年龄分别为-11.4 ~-1.4和1.27-1.90Ga;晚中生代火山层序的特征反映了古太平洋板块俯冲作用的不同影响。研究表明，在128- 122 Ma的第一次裂孔期，俯冲方式由低角度前向俯冲转变为中角度前向俯冲;在120- 110 Ma的第二次裂孔期，俯冲方式由高角度后滚俯冲转变为快速俯冲。
Zircon U–Pb and Hf isotope compositions have been systematically measured to constrain the timing and petrogenesis of the Late Mesozoic volcanic sequences in southeastern Zhejiang, SE China. The Early Yanshanian (Jurassic) volcanism took place at 177Ma and formed scattered volcanic rocks in the region. In contrast, the large-scale Late Yanshanian (Cretaceous) volcanism, with multiple eruptive stages between 140 and 88Ma, formed the widespread lower and upper volcanic series. Two volcanic hiatuses were clearly identified at 120–110Ma between the lower and upper volcanic series and at 128–122Ma between the two subdivided cycles within the lower series. In addition, the magnitude of the two volcanic cycles in the lower series is significantly different. The cycle I of the lower series (140–128Ma) occurred in the largest scale, which is much larger than the cycle II (122–120Ma) as well as the whole upper series (110–88Ma). Petrogenetically, the widespread Late Mesozoic volcanic rocks were mainly derived from the partial melting of the Paleoproterozoic crustal basement materials, with obvious addition of juvenile materials after 122Ma. The analyzed zircons of the Early Yanshanian volcanic rocks show crustal model ages (TDM2) mainly of 2.00–2.16Ga, and weighted mean εHf(t) value of −13.4. The εHf(t) and TDM2values are ca. −10 and 1.67–2.00Ga for zircons from the cycle I volcanic rocks, −11.4 to −1.4 and 1.27–1.90Ga for those from the cycle II volcanic rocks, −9.3 to −2.7 and 1.33–1.78Ga for those from the acidic rocks of the upper series, respectively. The characteristics of the Late Mesozoic volcanic sequences indicate the varying influence of the subduction of the paleo-Pacific plate. Our study supports that the subduction style changed from low-angle to intermediate-angle forward subduction at the first hiatus of 128–122Ma and then dramatically changed to rapid high-angle rollback subduction at the second hiatus of 120–110Ma.